Network security management is becoming a more difficult problem as networks grow in size and become a more integral part of society. Attacks on networks are growing due to both the intellectual challenge such attacks represent for hackers and the increasing monetary payoff for the serious attacker. Computer network attacks can take many forms and any one attack may include many different attack types. These attacks can create network damage through mechanisms such as viruses, worms, or Trojan horses, or overwhelming the network's capability in order to cause denial of service, and so forth.
Denial of service attacks are attempts to prevent legitimate users from utilizing or gaining access to computing resources, such as network bandwidth, memory, and CPU bandwidth. Thus, denial of service attacks make a computer resource unavailable to its intended users. Although any shared computer resource could potentially be at risk, typical targets of such attacks include high-profile web servers.
Another type of attack is the computer virus. A computer virus is a computer program that can copy itself and infect a computer without permission or knowledge of the user. Some viruses are programmed to damage the computer by damaging programs, deleting files, or reformatting the hard disk. Other virus programs are not designed to do any damage, but simply replicate themselves and perhaps make their presence known by presenting text, video, or audio messages. Even these less sinister malware programs can create problems for the computer user. They typically take up computer memory used by legitimate programs. As a result, they often cause erratic behavior and can result in system crashes.
Worms and Trojan horses are yet another type of attack. A worm can spread itself to other computers without needing to be transferred as part of a host, and a Trojan horse is a file that appears harmless. Worms and Trojans may cause harm to either a computer system's hosted data, functional performance, or networking throughput, when executed. In general, a worm does not actually harm either the system's hardware or software, while at least in theory, a Trojan's payload may be capable of almost any type of harm if executed.